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Many of the points which have been introduced above are collected in the following procedure:
2134 setrun (p)
{
register struct proc *rp;
rp = p;
rp->p_wchan = 0;
rp->p_stat = SRUN;
if (rp->p_pri < curpri)
runrun++;
if (runout != 0 &&
(rp->p_flag & SLOAD) == 0) {
runout = 0;
wakeup (&runout);
}
}
Check your understanding of “C” by figuring out what this one does.
There are two additional features you may need to know about:
“&&” is the logical conjunction (“and”) for relational expressions. (Cf. “||” introduced earlier.)
The last statement contains the expression
&runout
which is syntactically an address variable but semantically just a unique bit pattern.
This is an example of a device which is used throughout UNIX. The programmer needed a unique bit pattern for a particular purpose. The exact value did not matter as long as it was unique. An adequate solution to the problem was to use the address of a suitable global variable.
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